Sears’ shares were sent into a tailspin on Monday after it was announced that investor Bruce Berkowitz, the company’s largest outside shareholder at and a rare defender of the retailer’s so far unsuccessful attempts to turn itself around, was leaving the company’s board.

Berkowitz, a long-time investor, will step down from the Sears board at the end of the month, barely more than a year and a half after joining, Sears said in a press release. According to Bloomberg, his firm Fairholme Capital Management owned 27 million Sears shares as of Oct. 12. (or 25% of outstanding shares.) He was an early investor getting in in 2005 when Sears Holdings was created via the merger of Sears department stores and Kmart discount stores. Almost two years ago, Berkowitz signaled he would become more active as an investor and later joined the board.

Sears has lost about $11 billion since 2011 and in recent years has been selling off many of its best assets, including popular brands and many of its better store locations, to stave off a financial crunch. Berkowitz, in his letter to investors in January, recognized the erosion in Sears’ business but also said “there is still much left and the company is fixing its cash drain.”

Those challenges continued in its most recent quarter: Sears Holdings, which includes Kmart, saw a companywide decline of 11.5% in comparable sales, that were far deeper than those of Macy’s and J.C. Penney. Sears Holdings CEO Eddie Lampert, a hedge fund manager, has insisted he is reinventing Sears into a membership-based retailer with fewer and smaller stores though the sales and cash bleed have persisted. Lampert told investors in May the company is “fighting like hell” to get through its current turmoil. And it has continued to close hundreds of Sears and Kmart stores.

Still, Sears in March recognized doubts in the marketplace about its long-term future and concerns about a possible bankruptcy, In addition to selling off assets like its Lands’ End clothing brand, hundreds of stores, and its Craftsman brand, Sears has borrowed hundreds of millions from Lampert and recently said it would start selling its Kenmore appliances on Amazon.com to extend that brand’s reach.